need pix

I'm far from an expert, but mushy is pretty much never good in plant tissue, and monsteras shouldn't be wet and mushy. I would say that would be indicative of an issue.

It does sound like a fungal infection caused by any of several species of fungi grouped under the umbrella of 'damping-off diseases'. It's common for these infections to make their way into stem tissue where they clog the plant's plumbing (so to speak) and prevent normal flow of water and nutrients to the top of the plant.

Al